1. Field of the Invention
The present invention relates to radar and a method for enabling an array antenna.
2. Description of Related Art
An array antenna is an antenna system composed of a plurality of the same antennas arranged according to a particular pattern and is widely used in radar systems, such as a microwave/millimeter wave radar system. In conventional techniques, the antenna array may be implemented as a multiple input multiple output (MIMO) array antenna or a phased array antenna.
In conventional techniques, the MIMO array antenna may transmit, for example, a signal by a method of delaying the transmitting time. And, a receiving terminal of the MIMO array antenna may identify the signal reflected from different obstacles through a suitably selected transmitting time difference. In addition, the MIMO array antenna may also form a new virtual array antenna by the different placement locations of the antenna, thereby enhancing the angular resolution.
On the other hand, the phased array antenna uses a large number of independently controlled small antenna elements (typically referred to phase shifters) arranged on an antenna array surface, synthesizing the main lobes of different phases (directions) by controlling the transmitting time difference of each of the antenna elements. More specifically, an electromagnetic wave is transmitted by each of the phase shifters of the phased array antenna so as to strengthen the constructive interference and synthesize to one nearly straight radar main lobe, and the side lobes are significantly reduced due to the destructive interference. When operating the phased array antenna, the control system thereof may transmit a required lobe direction to a lobe control unit. Then, the lobe control unit may calculate the transmission time of the electromagnetic wave by each of the phase shifters and issue a command to the phase shifters, such that the electromagnetic wave emitted by each of the phase shifters interfere with each other to form the required lobe. Since a main lobe with higher gain may be produced, the phased array may achieve a longer detection distance.
Even though the MIMO array antenna and the phased array antenna have a high angular resolution and a long detection distance advantage respectively, the MIMO array antenna and the phased array antenna also have a shortcoming in a short detection distance and a low angular resolution respectively on the contrary. Therefore, if the features of the two kinds of antenna arrays may be integrated such that each of the antenna arrays may exert effects thereof at suitable timings, the performance of radar detection may be improved effectively.